Blast nozzle units with radial holes for self-blasting compressed gas electric circuit-breakers

ABSTRACT

A nozzle assembly for a compressed gas axial blast circuit breaker having a convergent inlet section, a divergent outlet section and an intermediate convergent section of smaller diameter than either the inlet or outlet sections. The intermediate section has radial holes, the mouths of which open into the gas flow stream and the outlet section has a plurality of annular rings of triangular cross-section, the cross-sectional areas decreasing and the spacing between adjacent rings increasing in a downstream direction of the outlet section.

United States Patent [191 Y Teijeiro 1*June 11, 1974 UN I 1 BLAST NOZZLE UNITS WITH RADIAL HOLES FOR SELF-BLASTING COMPRESSED GAS ELECTRIC CIRCUIT-BREAKERS Inventor: Benito J. Y Teijeiro, Bergamo, Italy Assignee: Magrini-Fabbriche Riunite Magrini Scarpa e Magnano M.S.M. S.p.A., Milan, Italy Notice: The portion of the term of this V,

' patent subsequent to June 13, 1989,

has been disclaimed.

Filed: July 26, 1972 Appl. No.: 275,219

Foreign Application Priority Data July 30, 1971 Italy 26987/71 US. Cl 200/148 A Int. Cl. H0lh 33/82 Field of Search 200/148 A [56] References Cited UNITED STATES PATENTS 3,291,948 l2/l966 Telford 200/l48 A 3,67(),l25 6/l972 Y Teijeiro ZOO/I48 A Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A nozzle assembly for a compressed gas axial blast cir cuit breaker having a convergent inlet section, a divergent outlet section and an intermediate convergent section of smaller diameter than either the inlet or outlet sections. The intermediate section has radial holes, the mouths of which open into the gas flow stream and the outlet section has a plurality of annular rings of triangular cross-section, the cross-sectional areas decreasing and the spacing between adjacent rings increasing in a downstream direction of the outlet section.

12 Claims, 1 Drawing Figure BLAST NOZZLE UNITS WITH RADIAL HOLES FOR SELF-BLASTING COMPRESSED GAS ELECTRIC CIRCUIT-BREAKERS BACKGROUND OF THE INVENTION 1. Field of Invention The present invention relates to improvements in blast nozzle units with radial holes for self-blasting compressed gas electric circuit-breakers which provides substantial improvement in the performance of the interruption-chambers employed in circuitbreakers of this type.

2. The Prior Art The compressed gas type electric circuit-breakers and the features of the axial blast interruptionchambers used in these circuit-breakers are already known and known criteria are used to determine the shapes of these interruption-chambers.

Particularly known are the interruption-chambers internally shaped in such a way to present, in the direction of the quenching gas outflow, an initial convergent zone, an intermediate zone having the smallest section, and an end divergent zone.

In the known types of chambers, the intermediate zone of smallest section may be either shaped only as an area of the plane defined by the intersection of the initial convergent zone with the end divergent zone or it may assume a cylindrical shape. In the latter case, said zone has a determined axial development and it constitutes the fillet length between the initial convergent and the end divergent zones, which are kept spaced from each other by the intermediate cylindrical zone of smallest section.

In both cases, holes are formed in with the zone of smallest section, which holes pass radially through the wall of the interruption-chamber in the transverse direction with respect to the central longitudinal axis of the chamber; these holes promote the decompression of the interruption-chamber part placed downstream of the first (convergent) zone. More particularly, the holes are located in the initial part of the third (divergent) zone immediately downstream of the second (smallest) zone when the latter is constituted only by a plane as previously described; on the contrary, they are located in the zone of smallest section when this one has a cylindrical shape and a non-zero axial development.

A further known characteristic of such compressed gas interruption-chambers is the presence of annular channels or grooves formed on the wall of the divergent zone, which also constitutes the end part of the chamber. These grooves are provided for the purpose of increasing the streamline of the quenching gases through the chamber.

The annular or ring-like grooves of previous interruption chambers have all been formed of a rectangular or similar diametral cross-section, all of the circular grooves having the same cross-sectional dimension.

It has been noted, however, that the known embodiments, described in general above, have several drawbacks, which are more or less important depending upon the actual construction. These drawbacks may take the form of a gas suction through the holes machined through the walls of the chamber or of a reduced outflow through the holes themselves which greatly hinder the decompression effect in the intermediate zone of the interruption-chamber, such decompression being the purpose of the holes passing through the walls of the chamber itself. Another problem is the formation of more or less considerable gaseous whirls in the end part (the divergent zone) of the chamber which adversely affect the direction of the gas stream which is axial and directed towards the interruptionchamber outlet.

Another drawback can be ascribed to the ring-like grooves having a rectangular diametral cross-section. Owing to the strong heating due to the electric are, even the materials making up the interruption-chamber suffer a decomposition which provokes a flow of decomposition gases. The development of these decomposition gases occurs according to elementary lines which, owing to the above-mentioned shape of the ringlike grooves, give rise to a resultant which hinders the axially directed flow of the quenching gas stream; the decomposition gas flow is directed perpendicularly with respect to the quenching gas flow.

Other-attempts at providing a different shape for the ring-like grooves, in order to eliminate this problem, have resulted in no appreciable change for the better.

SUMMARY OF THE INVENTION The object of this invention is therefore the construction of an interruption-chamber for compressed gas circuit-breakers structurally improved with respect to the prior art technique and in particular with respect to the interruption-chambers with radial holes.

A further object of this invention is to provide an interruption-chamber for electric circuit-breakers having improved decompression of the smallest sectioned intermediate zone to aid in the escape of quenching gas through holes machined radially in the walls of the intermediate section.

A further object of this invention is to improve the interruption-chambers in such a way that the ring-like grooves formed on the inner walls of the interruptionchambers assist in directing the discharge flow of the quenching gases.

A still further object of the present invention is an axial blast interruption-chamber combining the effects of quick decompression in the inlet zone of the radial holes and optimization of the flow of the decompression gases and the quenching gas through the downstream part of the chamber itself, consequently accelerating the outflow of the whole of these gases through the outlet orifice of the chamber and decreasing the whirl effects occurring in the total outflow, thereby greatly improving the performance of the interruptionchamber.

These and other objects, which will be apparent to one skilled in the art from the following detailed description, are best obtained by an axial blast interruption-chamber for self-blasting compressed gas electric circuit-breakers, especially circuit-breakers in which sulphur hexafluoride gas is used as the electric arc quenching fluid, having a blast nozzle structure, with radial holes, internally shaped to provide in the outlet direction a first substantially conical and convergent zone, a second intermediate zone of smaller section with respect to the other internal zones, and a third substantially conical and divergent zone. The latter zone has a length L determined by the known experimental relation, L B U,,/ 3 (1.5) V7; the intermediate zone of smallest section is substantially a convergent truncated cone zone with a very small tapering angle, the usual decompression holes being formed through the same second or intermediate zone, their mouth sections being inclined by an angle with respect to the chamber axis and, consequently, also with respect to the lines of the quenching gas flow; the mouth sections are also formed to be directed towards the interruption-chamber inlet. Finally, a plurality of annular grooves are formed downstream of the intermediate truncated-cone zone, the diametral crosssection of the grooves being substantially triangular shaped with a vertex angle defined by the meeting of two surfaces, one of the surfaces being substantially perpendicular to the axis of the chamber itself, and having an open base faced towards the outlet orifice of the interruption-chamber, namely directed in way to favor the escape of the decomposition gases along a direction concomitant with the direction of flow of the quenching gas stream; the dimensions of the substantially triangular diametral cross-section of each annular or ring-like groove decrease little by little from the first groove, immediately downstream the intermediate zone, to the last groove closer to the chamber outlet, with the distance between adjacent grooves increasing among successive grooves in the direction of the chamber outlet.

BRIEF DESCRIPTION OF THE DRAWING The improvement according to the present invention will be hereinafter described in greater detail with reference to the attached drawing, the only FIGURE appearing therein representing, in a schematic form and according to a longitudinal section, the nozzle unit with radial holes which is the subject of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the figure, the improved nozzle unit with radial holes of the present invention has a substantially truncated cone shaped intermediate zone 5, convergent towards the outlet 2 of the interruptionchamber and having a very limited cone-shape, the angle 20: which defines the cone-shape having values ranging from 2 to 10, but preferably having value of 4. Zone 5 has decompression holes 6 located therein.

The diameter of the mouth section of hole 6, which is directed in accordance with the axis YY ofthe interruption-chamber itself, forms an angle a a 0 with the axis YY in the direction opposed to the gas flow (which is directed towards the chamber outlet 2 according to the flow lines parallel to the axis YY; see arrows 7); therefore, it may be said, for the sake of brevity, that the mouth, or inlet, sections 10 of the holes 6 appear to be slanting by an angle a 0 towards the inlet 19 of the chamber, with respect to the axis YY and therefore also with respect to the lines of gas flow.

In this'way, an attraction zone is formed which facilitates the entry of a part of the flow 7 into the holes 6 (see arrows 8) to assure the quickest possible decompression of the zone 5, without, at the same time, giving rise in the same zone to a depression such as to introduce a gas suction from the outside through the holes 6, with the negative consequences which have already been discussed above.

The intermediate zone 5 remains substantially the zone of smaller section with respect to the other two zones, namely the upstream zone (zone I) and the downstream zone (zone 9); it is noted, however, that the smallest cross-section of the zone 5 is that one lying in the plane (perpendicular to the plane of the drawing) indicated by the line XX and defined by the intersection of the intermediate zone 5 itself (which is slightly convergent towards the nozzle outlet 2) with the end zone 9 which is conical and divergent.

A series of ring-like grooves 13 are machined in the internal wall of divergent zone 9. The grooves 13 have a substantially triangular diametral cross-section and a width and depth which decrease gradually from the first groove, immediately downstream the intermediate zone 5, to the last groove closer to the chamber outlet 2; furthermore, of the two sides of the triangular section formed by the wall of the chamber (wherein the grooves have been formed), one lies in a plane substantially perpendicular to the axis YY of the chamber itself, while the other slants (with respect to said plane perpendicular to the axis YY) by an angle 'y of between 40 and 50, with a preferred value y The third side of the triangular diametral cross-section of these ring-like grooves is merely ideal and is represented by the fully rectilinear outline of the inner part of the diametral cross-section of the divergent zone 9 supposed without any groove 13.

The distance or interval between the first grooves (that is, the distance between the exit edge of one groove and the entrance edge of the next adjacent groove, considered in the direction of flow of the gas stream), immediately downstream the intermediate zone 5, gradually increases among the successive grooves (the first grooves being considered as disposed in a practically continuous sequence, one after the other, with a substantially zero interval). Further, all the grooves have a single diameter, defining their annular dimension, this characteristic determining, in combination with the divergent cone-shape of zone 9, the different depths of the grooves; thus the apexes of the triangular diametral cross-sections (conicident with the maximum depth of the grooves) can be considered as lying in a single cylindrical ideal surface having the diameter D The outline created in the cross-section of the conical and divergent end zone 9 by the presence of the ring-like grooves 13 formed according to the abovedescribed teaching results in greatly increasing the streamline through the interruption-chamber, thereby reducing the occurrence of whirls to a minimum while conveying the decomposition gases in a direction concomitant with that of the deionizing (or quenching) gas.

The decomposition gases develop, from the material setting up the walls of the interruption chamber, according to elementary flow lines substantially perpendicular to the various surfaces of the walls; it is therefore evident, as the drawing shows, that in the nongrooved part of the conical divergent zone 9 each single elementary flow line has a direction concomitant with the quenching gas flow direction, while, as to the single grooves (whose wall, inclined by the angle y, gives rise to elementary flow lines directed in opposition to the quenching gas) it is the resultant of the single elementary flow lines which acts in the direction concomitant with the quenching gas, inasmuch as there is a vectorial sum between the elementary flow lines coming from the wall inclined by angle 7 and the elementary flow lines coming from the Wall lying in the plane perpendicular to the axis YY of 'the chamber.

The phenomenon of the decomposition gas generation from the material constituting the nozzle walls is one of the most important factors which determines the shape of the end zone 9 according to the present invention and, in particular, the number, width and distribution of the ring-like grooves 13 along this zone.

It is useful to arrange the deeper and wider circular grooves 13 closer to one another (up to disposing them in a direct succession with almost no intermediate spacing), immediately downstream the intermediate zone 5, inasmuch as the striking of the arc occurs in this zone and there is, therefore, the greatest production of heat; wider, deeper and more numerous grooves allow the formation of a greater volume of decomposition gases and therefore a wider and more effective collaboration of these gases with the quenching gas in their global action on'the arc.

Wider and deeper grooves give rise, logically, to resultants of elementary flow lines having a greater bulk which, besides interacting better with the quenching gas, have a suction effect on the resultants of lower bulk coming from the smaller ring-like grooves 13, located downstream of the previous ones, with the result of further increasing the interaction between the two types of gas (quenching and decomposition) besides obtaining a very regular conveying of the total resulting flow.

Also the range of the values of the angle 3 between 40 and 50, andpreferably 45, has been determined in connection with the phenomenon of the decomposition gas generation.

With angles 'y lower than 40, the resultant of the elementary flow lines would have directions less favorable to the concomitance and therefore to the interaction with the quenching gas flow; on the contrary, with angles greater than 50, The resultant would have a more favorable direction, but the cross sectional outline of the resulting grooves would be more open, with a less irregular streamline through the interruption chamber, the grooves would be wider and more interspaced (therefore becoming less efficient), and moreover it would be impossible to keep the angle ,8 (which defines the cone-shape of the end zone 9) within the range of values determined to be the most suitable to contribute to the best performance of the nozzle unit.

With the above-described improvements, there is a full interaction between the decomposition gases and the quenching gas, which act as rapidly as possible on the electric arc struck between the moving contact 3 and the fixed contact of the circuit-breaker. In fact, the described improvements not only offer the abovedescribed advantages, but also improve electric arc quenching; the quenching gas flow is allowed to run over and to sw athe the arc nucleus in the most effective and extensive way, because the internal shape of the chamber is such that it greatly facilitates the outflow of quenching gas in way that the gas can follow the electric are very closely throughout the entire opening travel of the contacts (moving contact 3 and fixed contact 20).

In particular, the intermediate zone 5, having a slightly truncated cone-shape, extends the deionizing action of the quenching gas, thus theintermediate zone 5 and the end zone 9 allow for an increase in the capacity of the interruption throughout the contacts opening travel.

It was determined, through tests, that the number of ring-like grooves 13 necessary to give excellent performances to the nozzle-unit may range from two to 10, the preferred number of these grooves being between four and six.

The portion of the divergent zone 9 containing the grooves 13, when the number of grooves is not higher than 10, turns out to have an axial extension less than or at the most equal to two-thirds L, wherein L is the length of the whole zone 9.

It was noted earlier that the performance and effectiveness of interruption-chambers of this type were considerably increased when the dimension L is found by the known experimental formula: L U,,/ 3 (1.5) 2, wherein U stands for the circuit-breaker rated voltage, in kV, and the length L is stated in mm.

'have been noticed with angle 28 having a value between 14 and 20, the most suitable value having been determined as 17.

The type of nozzle described herein isdesigned to be utilized with any type of compressed gas meeting the characteristics imposed by its use in an electric circuitbreaker, and particularly the dielectric requirements. The preferred embodiment of the present invention is most suitable for use with sulphur hexa-fluoride (SP as the arc quenching fluid, whose particularly good quenching characteristics are effectively added to those exhibited by the concerned nozzle.

Evidently, modifications and alternatives can be brought to the invention as hereinabove described, exemplified, illustrated and hereunder claimed, without departing from the scope or meaning of the blast nozzle construction of this invention.

What is claimed is:

l. A blast nozzle assembly, for self-blasting compressed gas electric circuit breakers having axial blast interruption chambers, comprising:

a substantially conical and convergent inlet zone;

a substantially conical and divergent end zone, having length L determined by the formula L U,,/ Vii (1.5) V7;

an intermediate truncated-cone shaped convergent zone located between said inlet and end zones;

a plurality of radially extending decompression holes formed in said intermediate zone, the mouth sections of said holes opening into said interruption chamber forming an angle a 9 0 with respect to the axis of said interruption chamber in the direction toward said inlet zone; and

a plurality of annular grooves formed in said divergent end zone downstream of said intermediate said tapering angle is approximately 4.

zone, said grooves each having: a substantially triangularly shaped diametral cross-section with a vertex angle defined by the meeting of two surfaces of the wall of said end zone, one of said surfaces being substantially perpendicular to said axis of said interruption chamber; and an open base directed toward the outlet end of said interruption chamber, the dimensions of said triangularly shaped cross-sections decreasing from the first groove immediately downstream of said intermediate zone to the last groove furtherest downstream of said intermediate zone and closer to the chamber outlet, the spacing between succeeding grooves increasing in the direction of the chamber outlet.

2. A nozzle assembly according to claim 1, wherein the tapering angle of said intermediate zone is between and 10.

3. A nozzle assembly according to claim 2, wherein 2O 4. A nozzle assembly according to claim 2, wherein the smallest cross section of said intermediate zone lies I in the plane defined by the intersection between said intermediate zone and said divergent end zone.

5. A nozzle assembly according to claim 4, wherein the tapering angle of said divergent end zone is be- 8 tween 14 and 20.

6. A nozzle assembly according to claim 5, wherein said tapering angle of said divergent end zone is approximately 17.

7. A nozzle assembly according to claim 5, wherein the vertex angle of said triangularly shaped crosssection of said annular grooves is between 40 and 50.

8. A nozzle assembly according to claim 7, wherein said vertex angle is approximately 45.

9. A nozzle assembly according to claim 7, wherein said annular grooves have the same annular diameter.

10. A nozzle assembly according to claim 9, wherein the number of said annular grooves is between 2 and 10.

11. A nozzle assembly according to claim 10, wherein the number of said annular grooves is between 4 and 6.

12. A nozzle assembly according to claim 10, wherein said annular grooves are contained in a portion of said divergent end zone which has an axial length not exceeding two-thirds of the total length of said divergent end zone.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 816 684 Dated June 11, 1974 V BENITO JOSE CALVINO V TEIJEIRO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Item [19] under United States Patent Y Teijeiro should read Calvi'ffo y Teijeiro Item [75] Benito J. Y. Teijeiro should read Benito 'Calvifio y Teijeiro and 3,670,125 6/1972 calvifio y Teijeiro Signed and sea led this 1st day of April 197.5.

C. Z-iARSHALL DANE? C. .LAJOL comzmsslonezr oi Patents and Trademarks USCOMM-DC 60376.5;51;

* KLS. GOVERNMENT PRINTING OFFICE Di, 0*366-334.

ORM PO-105O (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,816,684 Dated June 11, 1974 Invent fls) BENITO JOSE CALVINO v TEIJEIRO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Item [19] under United States Patent Y Teijeiro should read Calviffo y Teijeiro Item [75] Benito J. Y. Teijeiro should read Benito 'Calviio y Teijeiro and Item [56] under References Cited, line 4,

"3,670,125 6/1972 Y Teijeiro" should read 3,670,125 6/1972 calvifio y Teijeiro Signed and sealed this lst day of April 1975.

[p -\q 1' u' an...

attest:

C. IMP-SHALL DAM? *1 r2'- r 1- m); C. -iAsOr- Comzmsuoner o1 ants .attestzm: CfJIer and Trademarks FORM PO -150 (10-69) USCOMM,DC 037a,;mm

U.5. GOVERNMENT PRINTlNG OFFICE: l9! 0-356-335. 

1. A blast nozzle assembly, for self-blasting compressed gas electric circuit breakers having axial blast interruption chambers, comprising: a substantially conical and convergent inlet zone; a substantially conical and divergent end zone, having length L determined by the formula L > OR = Un/ square root 3 . (1.5) . square root 2; an intermediate truncated-cone shaped convergent zone located between said inlet and end zones; a plurality of radially extending decompression holes formed in said intermediate zone, the mouth sections of said holes opening into said interruption chamber forming an angle Alpha NOT = 0 with respect to the axis of said interruption chamber in the direction toward said inlet zone; and a plurality of annular grooves formed in said divergent end zone downstream of said intermediate zone, said grooves each having: a substantially triangularly shaped diametral cross-section with a vertex angle defined by the meeting of two surfaces of the wall of said end zone, one of said surfaces being substantially perpendicular to said axis of said interruption chamber; and an open base directed toward the outlet end of said interruption chamber, the dimensions of said triangularly shaped cross-sections decreasing from the first groove immediately downstream of said intermediate zone to the last groove furtherest downstream of said intermediate zone and closer to the chamber outlet, the spacing between succeeding grooves increasing in the direction of the chamber outlet.
 2. A nozzle assembly according to claim 1, wherein the tapering angle of said intermediate zone is between 20* and 10*.
 3. A nozzle assembly according to claim 2, wherein said tapering angle is approximately 4*.
 4. A nozzle assembly according to claim 2, wherein the smallest cross section of said intermediate zone lies in the plane defined by the intersection between said intermediate zone and said divergent end zone.
 5. A nozzle assembly according to claim 4, wherein the tapering angle of said divergent end zone is between 14* and 20*.
 6. A nozzle assembly according to claim 5, wherein said tapering angle of said divergent end zone is approximately 17*.
 7. A nozzle assembly according to claim 5, wherein the vertex angle of said triangularly shaped cross-section of said annular grooves is between 40* and 50*.
 8. A nozzle assembly according to claim 7, wherein said vertex angle is approximately 45*.
 9. A nozzle assembly according to claim 7, wherein said annular grooves have the same annular diameter.
 10. A nozzle assembly according to claim 9, wherein the number of said annular grooves is between 2 and
 10. 11. A nozzle assembly according to claim 10, wherein the number of said annular grooves is between 4 and
 6. 12. A nozzle assembly according to claim 10, wherein said annular grooves are contained in a portion of said divergent end zone which has an axial length not exceeding two-thirds of the total length of said divergent end zone. 